[APInt] Rewrite getLoBits in a way that will do one less memory allocation in the multiword case. Rewrite getHiBits to use the class method version of lshr instead of the one in APIntOps. NFCI

llvm-svn: 299243

2 files changed, 22 insertions, 3 deletions

diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index 37ad30981d1..8ac881e4c7f 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -724,13 +724,14 @@ bool APInt::isSplat(unsigned SplatSizeInBits) const {
 
 /// This function returns the high "numBits" bits of this APInt.
 APInt APInt::getHiBits(unsigned numBits) const {
-  return APIntOps::lshr(*this, BitWidth - numBits);
+  return this->lshr(BitWidth - numBits);
 }
 
 /// This function returns the low "numBits" bits of this APInt.
 APInt APInt::getLoBits(unsigned numBits) const {
-  return APIntOps::lshr(APIntOps::shl(*this, BitWidth - numBits),
-                        BitWidth - numBits);
+  APInt Result(getLowBitsSet(BitWidth, numBits));
+  Result &= *this;
+  return Result;
 }
 
 unsigned APInt::countLeadingZerosSlowCase() const {
diff --git a/llvm/unittests/ADT/APIntTest.cpp b/llvm/unittests/ADT/APIntTest.cpp
index f05cbb9d915..51c6347cbe8 100644
--- a/llvm/unittests/ADT/APIntTest.cpp
+++ b/llvm/unittests/ADT/APIntTest.cpp
@@ -1958,3 +1958,21 @@ TEST(APIntTest, setAllBits) {
   EXPECT_EQ(128u, i128.countTrailingOnes());
   EXPECT_EQ(128u, i128.countPopulation());
 }
+
+TEST(APIntTest, getLoBits) {
+  APInt i32(32, 0xfa);
+  i32.setHighBits(1);
+  EXPECT_EQ(0xa, i32.getLoBits(4));
+  APInt i128(128, 0xfa);
+  i128.setHighBits(1);
+  EXPECT_EQ(0xa, i128.getLoBits(4));
+}
+
+TEST(APIntTest, getHiBits) {
+  APInt i32(32, 0xfa);
+  i32.setHighBits(2);
+  EXPECT_EQ(0xc, i32.getHiBits(4));
+  APInt i128(128, 0xfa);
+  i128.setHighBits(2);
+  EXPECT_EQ(0xc, i128.getHiBits(4));
+}